Highly alkaline dichlorodimethylhydantoin bleaching solutions and methods



May 31, 1960 R. A. BLOMFIELD HIGHLY ALKALINE DICHLORODIMETHYLHYDANTOINBLEACHING SOLUTIONS AND METHODS Filed Feb. 25, 1957 EFFECT OF pH OFBLEACH COMPOSITION ON BLEACH I NC EFFECTIVE N ESS OO SODIUM HYPOGHLORITEE1 TRICHLOROCYANURIC ACID DICHLOROCYANURIC ACID 0DICHLORODIMETHYLHYDANTOIN o m m w w M65102. moz sw h mm RA. Blomfield IINVEN-TOR.

/T3'%?%'Z2-w Attorney HIGHILY ALKALINE DICHLORODIMETHYL- HY DANTOINBLEACHING SOLUTIONS AND METHODS Rodney A. Blornfield, Wyandotte, Mich.,assignor to Wyandotte Chemicals Corporation, Wyandotte, Mich., acorporation of Michigan No Drawing. Filed Feb. 25, 1957, Ser. No.642,142

Claims. (Cl. 8-108) This invention relates to an improved bleachcomposition and to an improved method for bleaching textiles. In a morespecific aspect, this invention relates to an improved bleachcomposition employing 1,3-dichloro-5,5- dimethylhydantoin as the sourceof available chlorine.

Bleaching operations conducted in commercial as well as in homelaundries which have been based on chlorinecontaining bleach compoundshave generally involved the use of various hypochlorites, such as sodiumhypochlorite or calcium hypochlorite. Such hypochlorites are effectivelow-cost bleaching agents, but they have certain disadvantages. The mostgenerally recognized disadvantage of hypochlorite bleaches is thetendency for such bleaches to react with cotton or linen fabric inaddition to reacting with the stain which is desired to be removed. Thereaction of the bleach with the fabric results in reduction in fabricstrength, particularly after the fabric has been subjected to repeatedwash cycles employing a hypochlorite bleach. This disadvantage isheightened by the fact that, while the stain removal activity of ableach is increased with increased temperature, the reaction ofhypochlorite bleaches with fabric is also increased at highertemperatures.

It is generally known, also, that the activity of hypochlorite bleachesis increased in acidic solutions, but such an increase in activity isone of which advantage cannot be taken in most laundry operations sincethe wash liquor is generally alkaline in nature. Furthermore, acidsolutions present problems in a washing process, such as the formationof greasy fatty acids in the presence of laundry soap and corrosion ofmetal parts. A bleaching compound which overcomes many of thedisadvantages associated with hypochlorite bleaches is l,3-dichloro-5,5-dimethylhydantoin, hereinafter referred to simply asdichlorodimethylhydantoin. Aqueous solutions ofdichlorodimethylhydantoin have the outstanding advantage as bleachcompositions of greatly reducing the loss of fabric strength associatedwith hypochlorite bleaches, while at the same time providing effective,but gentle, bleaching action. In the application of Maurice G. Kramer,Serial No. 482,698, filed January 19, 1955, a bleach composition basedon the combination of dichlorodimethylhydantoin and sodiumtripolyphosphate is disclosed and claimed which provides effectivebleaching action but with remarkably low reduction in fabric strength ofthe bleached fabric. It is there disclosed that the mixture can containfrom 8 to 75 weight percent dichlorodimethylhydantoin, based on theweight of the mixture, and that a particularly effective combination ofthese ingredients is one containing 75 weight percent sodiumtripolyphosphate and 25 weight percent dichlorodimethylhydantoin.

A need exists, however, for increasing the activity ofdichlorodimethylhydantoin, and thereby increasing its effectiveness as ableach, so that fuller advantage can be taken of this improved bleachingcompound in all types of bleach operations, and particularly in bleachopera- Egg 2,938,764

tions on heavily and stubbornly stained fabrics. The removal of suchstubborn stains, if accomplished at all, under conventional bleachpractices employing a hypochlorite bleach requires repeated applicationof the hypo-' chlorite bleach, or time-consuming soaks in highconcentrations of hypochlorites at low temperatures, both of whichoperations necessarily result in serious loss of fabric tensilestrength. An increase in eifectiveness of the dichlorodimethylhydantoinbleaching compound would have the equally important benefit, whenbleaching normally stained fabrics in a laundry, ofreducing'the numberof items requiring rewash and rebleach in order to of this invetnion arebased on the discovery that the bleaching effectiveness ofdichlorodimethylhydantoin is remarkably increased in aqueous solutionshaving a significantly higher pH than is customarily used in bleachingoperations. The elfectiveness of sodium hypochlorite and other bleachesbased on chlorine-containing compounds, on the other hand, is notincreased, and in some cases, is reduced in such highly basic solutions.

Bleaching operations are normally carried out in aqueous solutionshaving a pH of about 9.0 to 10.5. Increased basicity tends to stabilize,rather than activate, conventional hypochlorite bleaches, however. Ihave found that the effectiveness of dichlorodimethylhydantoin as ableach is significantly increased in aqueous solutions having a pH inthe range of 12 to 14, measured at 25 C. The improved bleach compositionof this invention is, therefore, a composition containingdichlorodimethylhydantoin, water and an alkalizing agent wherein thealkalizing agent is present in an amount sufficient that the hydrogenion concentration of the aqueous composition corresponds to a pH of 12to 14. The eifectiveness of bleaching agents is evaluated on the basisof change in light reflectance of unbleached muslin panels. On thisbasis, the composition of the invention and the method of the inventionalford a reflectance increase of as high as 40%, whereas an aqueoussolution of dichlorodi-meth ylhydantoin at a pH of about 10.5 affords areflectance increase of about 25%. Furthermore, the reflectance increaseof fabrics bleached with sodium hypochlorite is actually lower at thehigh pH range of this invention than at the conventional pH of 10 to10.5. An article by R. G. Ditzel et al., entitled ACL-SS, New activeingredient for Bleaching and Sanitizing Agents, Soap and ChemicalSpecialties, pp. -139, February 1956, reveals in Figure I on page 127that the reflectance increase of unbleached muslin bleached withtrichloroisocyanuric acid also decreases with increasing pH.

As was stated hereinabove, the improved bleach composition of thisinvention is an aqueous solution of dichlorodimethylhydantoin containinga sufiicient amount of an alkalizing agent. so that the hydrogen ionconcentration of the solution corresponds to a pH in the range from 12to 14. The alkalizing agent can be any alkaline-reacting substance, suchas the alkalizing agents already present in the wash liquor fromprevious operations of the wash cycle as well as any alkalizing agentthat can be added to an aqueous solution of dichlorodimethylhydantoin insuflicient quantity so that the desired pH is Patented May 31, 1960obtained. It will be apparent that many different alkalizing agents areavailable for this purpose. It will be further apparent that thespecific amount of alkalizing agent in the composition can only bedefined for a specific bleach operation since consideration must begiven to the efifect of other ingredients, such as soap and detergentswhich are often present during the bleach operation. The fabric load andthe characteristics of soil and stain involved also influence the amountand specific kind of alkalizing agent that is desirable. When given thebenefit of this disclosure, however, one is able to readily ascertainthe quantity of alkalizing agent which need be added to an aqueoussolution of dichlorodimethylhydantoin so that the composition of theinvention is obtained.

Any known alkalizing agent which will establish the desired pH can beused. .Alkali metal hydroxides, such as sodium and potassium hydroxide,particularly in combination with a bufiering'agent, such as sodiumcarbonate, are the most frequently used alkalizing agents. Examples ofother alkalizing agents that can be used are the alkali metal silicates,such as sodium metasilicate, either in anhydrous or pentahydrate form,sodium sesquisilicate or sodium orthosilicate. The alkalizing agent canbe a mixture of these materials and can include alkali metal fatty acidsoaps in combination with other alkalizing agents. The alkaline salts,such as sodium carbonate, which exhibit a buflfering action can beemployed in combination with the alkalizing agent, and examples of othersuch buffering salts are trisodium phosphate and tetrasodiumpyrophosphate.

The bleaching composition of this invention can be used alone or incombination with any conventional laundry detergent composition.Conventional ingredients for detergent or bleach compositions ofteninclude sodium carboxymethylcellulose and/or solvents, such as pine oilor kerosene, in addition to soap, detergents, alkaline builders, and thelike, and these are examples of the type of other materials that can bepresent without harmful efiect on the improved bleaching action of thecomposition of the invention.

A specific example of the type of detergent composition which can bepresent together with the bleach cornposition of this invention is thedetergent composition disclosed and claimed in U.S. 2,566,501 whereinthe detergent composition contains defined amounts of sodiumalkylbenzenesulfonate, sodium carboxymethylcellulose and an inorganicalkaline salt, such as sodium carbonate or modified soda.

It will be noted that, when the bleach composition of this invention isused together with a suds operation or closely following a sudsoperation in a wash cycle, the quantity of the alkalizing agent requiredto establish the desired pH is at least partly supplied by thealkalizing materials in the detergent composition used in the sudsoperation. In this situation, the quantity of alkalizing agent whichmust be added together with the aqueous solution ofdichlorodimethylhydantoin is simply. that amount necessary to establishthe pH of the composition of the invention. This latter step is theessence of one embodiment of the present invention, which is the methodof washing and bleaching wherein an aqueous solution ofdichlorodimethylhydantoin is added to the wash liquor together with asufiicient amount of an alkalizing agent so that the hydrogen ionconcentration of the wash liquor corresponds to a pH in the range of 12to 14.

It has been pointed out that the bleaching effectiveness of an aqueoussolution of dichlorodimethylhydantoin is significantly improved when thepH of the aqueous solution is in the range of 12m 14. It has been found,specifically, that heavily stained fabrics are most effectively bleachedunder practical conditions when the bleach composition of this inventioncontains the amount of alkalizing agent which establishes the pH at from12.2 to 12.5.

The amount of dichlorodimethylhydantoin employed in the composition ofthe invention is generally that amount which, when dissolved in water,provides from 12.5 to 3600 parts of available chlorine per million partsof water. Expressed on a weight percent basis, the amount ofdichlorodimethylhydantoin is from 0.0018 to 0.54 weight percent based onthe weight of dichlorodimethylhydantoin and water. .This is the broadrange of amount of dichlorodimethylhydantoin which provides bleachingaction and has utility for the wide variety of bleaching problems thatare met. Generally speaking, however, the amount ofdichlorodimethylhydantoin employed in the composition of the inventionis that amount which, when dissolved in water, provides from 50 to 1200parts of available chlorine per million parts of water. This range ofamount corresponds to a weight percent of 0.0075 to 0.18 based on theweight of dichlorodimethylhydantoin and water.

The following examples are supplied in order to illustrate theinvention, and should not be used to unduly restrict the invention asdisclosed herein.

EXAMPLE I The bleaching effectiveness of a composition according to theinvention was tested in a series of laboratory beaker tests conducted soas to determine the effect of pH under controlled conditions.

For comparative purposes, tests were made under the same conditions withsodium hypochlorite, dichlorocyanuric acid and trichloroisocyanuricacid.

The bleach compositions tested were prepared by dissolving a sufiicientquantity of the active agent in 1 liter of water so that theconcentration of the active agent was sufficient to provide 200 partsper million of available chlorine. Varying amounts of alkalizing agentswere then added so as to obtain the pH values indicated in Table 1below. v

The bleach composition based on dichlorodimethylhydantoin was preparedby dissolving in water a mixture of dichlorodimethylhydantoin and sodiumtripolyphosphate containing 25 weight percent dichlorodimethylhydantoin,based on the weight of the mixture, the amount of the mixture insolution being that amount which provided 200 parts per million ofavailable chlorine. This amount of dichlorodimethylhydantoin constituted0.03 weight percent based on the weight of water anddichlorodimethylhydantoin.

The bleaching tests were carried out on six 4" x 4" swatches ofunbleached muslin which were prepared for the tests by washing them 5minutes in a tergotometer at 75 cycles per minute at F. in a 0.25 weightpercent solution of a detergent composition consisting essentially ofsodium alkylbenzenesulfonate, sodium carboxymethylcellulose and aninorganic alkaline saltas set forth in U.S. Patent 2,566,501, citedabove, said detergent composition having been prepared in 1 liter ofdemineralized water. The swatches were then rinsed under a demineralizedwater tap.

After rinsing the washed swatches, the bleaching operation was carriedout in the tergotometer in the 1 liter bleach solutions, prepared asdescribed above, for 15 minutes at 75 cycles per minute at 160 F.

After bleaching, the swatches were removed from the bleach liquor,rinsed under the demineralized water tap and pressed dry.

The bleaching eifectiveness obtained in each test was measured bystandard light reflectance techniques. The light reflectance of thebleached swatches was compared to the light reflectance of the swatchesbefore bleaching using a blue filter in a Hunter multi-purposereflectometer manufactured by Henry A. Gardner Laboratory, Inc.,Washington, DC.

The results of these tests are summarized below in Table 1.

' Table 1 Efiect of pH of Bleach Composition on Bleaching EffectivenessDichlorodimethyl- Sodium Hypo- Dlchlorocy- Trichloroiso- Tes AlkalizlngAgent, grams hydantoin chlorite anurio Acid cyanuric Acid N 0. per literRefleot Reflect- Refiect- ReflectpH ance pH ance pH ance pH anceIncrease, Increase, Increase, Increase, Percent Percent Percent PercentSodium Triopolyphosphate- 7. 6 25. 3 Disodium phosphate, 5 8. 4 21. 9. 352. 0 8. 2 40. 7 8. 3 41. 8 Sodium bicarbonate, 9. 2 19. 0 9. 2 50. 2 8.8 36. 3 8.8 39. 6 gogum cargonage, 2.8 11. 2 30. 2 11. 6 54. 2

o umcar onae, 5 {g gi 3 5 2 2 11. 4 34. a 11.9 52. s

o um car ona e, {2 31 gi g fg 11. 5 a5. 0 12.1 52.5 o umcar one e,{Sodium hydroxide, M 12.0 35. s 12. 4 5o. 5 Sogum hydroxide: 12. 3 33. 2

o um car onate, {Sodium hydroxide 1 12. 4 37.3 12.6 51. 0

Sodium hydroxide, 3 12. 8 40.0 Sodium hydroxide, 5- 13. 0 39. 0 13. 146. 5 13. 1 36. 8 13. 1 41. 3 Sodium hydroxide, i0 13. 2 44. 4 Sodiumhydroxide, 30.- 13. 9 41.5 Sodium hydroxide, 50 14. 0 34. 3

The results of these tests, which are tabulated in Table 1 above, aregraphically illustrated in the accompanying drawing. The drawing aids inappreciating the unusual increase in bleaching effectiveness that oneobtains with the composition of the invention where the bleachcomposition comprises water, dichlorodimethylhydantoin and a suflicientamount of an alkalizing agent so that the hydrogen ion concentration ofthe composition corresponds to a pH in the range from 12 to 14. Aparticularly desirable range of pH for the composition of the inventionis 12.5 to 13.5. This latter range afforded the optimum bleaching actionin the tests carried out in this example. No such increase in bleachingeffectiveness at high pH is obtained with sodium hypochlorite,dichlorocyanuric acid or trichloroisocyanuric acid, and in fact, thebleaching effectiveness of these compounds is slightly decreased at thehigh pH.

EXAMPLE II The results of the tests carried out in the laboratory,described in Example I, were confirmed in practical washing andbleaching operations using an 18 pound fabric load in a Prosperitywashing machine. The fabric load for each test was 18 pounds of heavilysoiled and stained fabrics from a commercial laundry. In addition to theheavily soiled and stained fabrics from the commercial laundry,unbleached muslin swatches, prepared as described in Example I, wereincluded in the fabric load so that reflectance increase measurementscould be made, also as described in Example I.

The general wash formula which was followed in these tests is set forthbelow in Table 2.

Operation Water, Soil:

Time, Level, Minutes Temperinches ature,

1 Approximate. 1 Steam added H H WOSOJNCJOOSNNOMMUIMN The total volumeof water employed for each of operations 1, 2, 4, 5, 7, 8, and 1013,including water required for saturation of the fabric, was 23.8 gallons,and the total volume of water employed for each of operations 3, 6, 9and 14, including water required for saturation of the fabric, was 16.2gallons.

Four washes were carried out according to the general wash formula setforth in Table 2. The bleach composition employed in operation No. 6 inwashes No. 2, 3 and 4 was in accordance with the present invention asindicated in Table 3 below, while the bleach composition used inoperation No. 6 in wash No. 1 was not in accordance with the presentinvention since there was not a suiiicient amount of alkalizing agentpresent so that the bleach composition had a pH in the range of 12 to14.

The composition used for break operation No. 3 in the general washformula in each of the four washes reported below in Table 3 was aproprietary composition based on a mixture of sodium hydroxide andsodium carbonate which also contained minor amounts of tetrasodiumpyrophosphate, sodium carboxymethylcellulose, deodorized kerosene andpine oil. The amount of this composition used in operation No. 3 in eachof the tests was 9.5 ounces.

The composition used for bleach-break operation No. 6 in washes Nos. 2,3 and 4 reported below in Table 3 was a mixture of the breakcompositiongiven above for operation No. 3 and a bleach compositionconsisting of a mixture of sodium tripolyphosphate anddichlorodimethylhydantoin containing 25 weight percentdichlorodirnethylhydantoin based on the weight of the lastmentionedmixture. The composition used for operation No. 6 in wash No. 1 reportedbelow in Table 3 was a mixture of dichlorodimethylhydantoin and sodiumtripolyphosphate containing 25 weight percent ofdichlorodimethylhydantoin based on the weight of the mixture.

The composition used for suds operation No. 9 was a mixture of the breakcomposition given above for operation No. 3 and a commercial laundrysoap which was an alkali-metal fatty acid soap derived from fatty acidshaving a titer of 39 to 42 C. and which contained a minimum of 92% realsoap. The amount of the break composition was 0.95 ounce and the amountof the soap was 0.24ounce in each of the tests.

The composition used for sour operation No. 14 was a laundry sourconsisting of sodium silicofluoride. The amount of the sodiumsilicofluoride used in each of the tests was 0.36 ounce.

in Table 3.

1 Dichlorodimethylhydantoin.

The weight percent of dichlorodimethylhydantoin in Washes Nos. 1, 2 and3 corresponds to 111' parts of available chlorine per million parts ofwater and the weight percent of dichlorodimethylhydantoin in wash No;4'cor responds to 222 parts of available chlorine per million parts ofwater.

said alkalizingagent so that the hydrogen ion concentration of saidcomposition corresponds to a pH in the range of 12 to 14.

2. An improved bleach composition, which comprises, 1,3-dichloro5,S-dimethylhydantoin, an alkalizing agent selected from the groupconsisting'of alkali metal hydroxides, alkali metal silicates andmixtures thereof and water, said composition containing a sufficientamount of said alkalizing agent so that the hydrogen ion concentrationof said composition corresponds to a pH in the range of 12.5 to 13.5.

3. An improved bleach composition, which comprises,1,3-dichloro-5,S-dimethylhydantoin, an alkalizing agent selected fromthe group consisting of alkali metal by droxides, alkali metal silicatesand mixtures thereof and water, said composition containing from about0.0018 to 0.54 weight percent of 1,3-dichloro-5,S-dimethylhydantoinbased on the weight of 1,3-dichloro-5,5-dimethyl I hydantoin and water,and said composition containing a The observation that the quality ofthe washed fabric in wash No. 1 was poor indicates that original stainswere clearly visible and that 50 to 75% of'the items in the wash wouldrequire rewash and rebleach.

The observation that the quality ofthe washed fabrics in washes Nos. 2and 3 was good indicates that the original stains were only occasionallyslightly visible and that from 10 to 15% of the items would requirerewash and rebleach. The plus sign beside good for wash No. 4 indicatesthat the quality of the washed fabrics was better than that of washesNos. 2 and 3 and that only about 5 to 10% of the items would requirerewash and rebleach.

I It should be emphasized that the original fabric load used in thetests reported in this example were heavily soiled and stained. Theresults shown above in Table 3 are a clear confirmation for the workreported in Example I showing that the bleach composition of theinvention, Water, dichlorodimethylhydantoin and sufficient alkalizingagent so that the composition has a pH in the range of 12 to 14, isremarkably improved. The data in Table 3 shows, further, that acomposition of the invention wherein the amount of alkalizing agentprovides a pH of 12.2 to 12.5 is an effective and desirable compositionfor use in bleaching heavily stained fabrics. It should be particularlynoted, in this regard that breakbleach operation No. 6 was carried outat about. 200 F. The composition of this invention is highly effectiveat such high temperatures, and in the method of this invention atemperature of 190 to 200 F. is very desirable for bleaching heavilysoiled and stained fabrics. Such high temperatures can be used with thebleach composition and method of this invention without the loss infabric strength which would occur if a hypochlorite bleach were used atsuch high temperatures. However, the method of this invention isgenerally applicable and the improved results are obtained when themethod is carried out at temperatures in the range of 140 to 210 F.

It should be apparent that the objectives of this invention have beenattained. The principal improvement lies in the increased bleachingeffectiveness one obtains with the bleach composition of the inventionwhile at the same time retaining the important advantage associated withdichlorodimethylhydantoin of much smaller reduction in fabric strengththan is encountered in the use of hypochlorite bleaches.

I claim:

1. An improved bleach composition, which comprises,1,3-dichloro5,S-dimethylhydantoin, an 'alkalizing agent selected fromthe group consisting of alkali metal hydroxides, alkali metal silicatesand mixtures thereof and water, said composition containing a sufiicientamount of sufficient amount of said alkalizing agent so that the hydrogen ion concentration of said composition is in the range of 12 to14.

4. An improved bleach composition, which comprises,

1,3-dichloro-5,S-dimethyIhydantoin, an alkalizing agent selected fromthe group consisting of alkali metal hydroxides, alkali metal silicatesand mixtures thereof and water, said composition containing from about0.0075 to 0.18 Weight percent of 1,3-dichloro-5,5-dimethfrlhydantoinbased on the Weight of 1,3-dichloro5,5-dimethylhydantoin and water, andsaid composition containing a sufficient amount of said alkalizing agentso that the hydrogen ion concentration of said composition is in therange of 12 to 14.

5. An improved'bleach composition, which comprises, Water, an alkalizingagent selected from the group consisting of alkali metal hydroxides,alkali metal silicates and mixtures thereof and a mixture of1,3-dichloro- 5,5-dimethylhydantoin and sodium tr'ipolyphosphate, saidmixture containing from 8 to 75' weight percent of1,CLdichloro-S,S-dimethylhydantoin based on the weight of said mixture,said composition containing 0.0018 to 0.54 weight percent of 1,3dichloro 5,S-dimethylhydantoin based on the weight of1,3-dichloro-5,5-dimethylhydantoin and Water, and said compositioncontaining a sufiicient amount of said alkalizing agent so that thehydrogen ion concentration of said composition corresponds to a pH of1.2 to 14.

6. A composition according to claim 5 wherein said mixture containsabout 25 weight percent 1,3-dichloro- 5,5-dimethylhyd'antoin based onthe weight of said mixture. i

7. An improved bleach composition, which comprises, water, an alkalizingagent seiected from the group con sisting of alkali metal hydroxides,alkali metal silicates and mixtures thereof and a mixture ofi,3-dichloro- 5,5-dimethylhydantoin and sodium tripolyphosphate, saidmixture containing about 25' weight percent 1,3-dichloro-5,5-din1ethylhydantoin based on the Weight of said mixture, saidcomposition containing'0L007 5 to 0.18 weight percent1,3-dichloro-5,S-dimethylhydantoin based on the weight of1,3-dichloro-5,5-dimethylhydantoin and Water, and said compositioncontaining a sufiicient amount of said alkalizing agent so that thehydrogen ion concentration of said composition corresponds to a pH of12.5 to 13.5. 1

8. An improved method for bleaching cotton fabrics, which comprises,agitating said fabrics in an alkaline aqueous bleach composition at atemperature in the range of about to 210 B, said aqueous bleachcomposition comprising water, an alkalizing agent selected from thegroup consisting of alkali metal hydroxides, alkali metal silicates andmixturesthereof and 1,3-dichloro- 5,5-dimethylhydantoin, the amount ofsaid alkalizing 9 to a pH in the range of 12 to 14, and the amount ofsaid 1,3-dichloro-5,5-dimethylhydantoin being from 0.0018 to 0.54 weightpercent based on the weight of 1,3-dichloro- 5,5-dimethylhydantoin andwater in said aqueous bleach composition.

9. A method according to claim 8 wherein said weight percent1,3-dichloro-5,5-dimethylhydantoin is from 0.0075 to 0.18 and whereinthe agitating of said fabrics in said aqueous bleach composition iscarried out at a temperature in the range of 190 to 200 F.

10. In a method of washing and bleaching cotton textiles wherein thetextiles are subjected in any sequence to washing, rinsing and bleachingoperations in an aqueous medium, the improvement which comprises,carrying out said bleaching operation by addingdichlorodimethylhydantoin and an alkalizing agent selected from thegroup consisting of alkali metal hydroxides, alkali metal silicates andmixtures thereof to said aqueous medium, the amount of saiddichlorodimethylhydantoin added being such as to constitute from 0.0018to 0.54 weight percent based on 10 the weight ofdichlorodimethylhydantoin and water in said aqueous medium, and theamount of said alkalizing agent added being sufiicient so that thehydrogen ion concentration of said aqueous medium corresponds to a pH of12 to 14.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES An Introduction to Textile Bleaching by Marsh, pub. byChapman and Hall, London (1948), pp. 78, 81, 82, 214424.

8. AN IMPROVED METHOD FOR BLEACHING COTTON FABRICS, WHICH COMPRISES,AGITATING SAID FABRICS IN AN ALKALINE AQUEOUS BLEACH COMPOSITION AT ATEMPERATURE IN THE RANGE OF ABOUT 140 TO 210*F., SAID AQUEOUS BLEACHCOMPOSITION COMPRISING WATER, AN ALKALIZING AGENT SELECTED FROM THEGROUP CONSISTING OF ALKALI METAL HYDROXIDES, ALKALI METAL SILICATES ANDMIXTURES THEREOF AND 1,3-DICHLORO5,5-DIMETHYLHYDANTOIN, THE AMOUNT OFSAID ALKALIZING AGENT BEING SUFFICIENT SO THAT THE HYDROGEN IONCONCENTRATION OF SAID AQUEOUS BLEACH COMPOSITION CORRESPONDS TO A PH INTHE RANGE OF 12 TO 14, AND THE AMOUNT OF SAID1,3-DICHLORO-5,5-DIMETHYLHYDANTOIN BEING FROM 0.0018 TO 0.54 WEIGHTPERCENT BASED ON THE WEIGHT OF 1,3-DICHLORO5,5-DIMETHYLHYDANTOIN ANDWATER IN SAID AQUEOUS BLEACH COMPOSITION.